--> When BGP router receives multiple paths to particular destination, then they will use BGP Path Selection Algorithm to select best path.
BGP Path Selection Algorithm
--> First of all BGP assigns the First Valid Path as BGP best path, then it compares the best path with next valid paths it received. ( Valid Path means the path which has next hop reachability).
--> Prefers the path which has highest weight.
---> Prefers the path which has highest local preference.
---> Prefers the path which is locally originated via network command compared to network is coming via redistribution .
IGP> Incomplete > Aggregate-Address
--> Prefers the path which is having shortest AS Path. ( If you want to skip this step, then you can give bgp bestpath as-path ignore)
--> Prefer the path with the lowest origin type
--> Prefer the path with the lowest multi-exit discriminator (MED).
--->Prefer eBGP over iBGP paths.
BGP Path Selection Algorithm
--> First of all BGP assigns the First Valid Path as BGP best path, then it compares the best path with next valid paths it received. ( Valid Path means the path which has next hop reachability).
--> Prefers the path which has highest weight.
---> Prefers the path which has highest local preference.
---> Prefers the path which is locally originated via network command compared to network is coming via redistribution .
IGP> Incomplete > Aggregate-Address
--> Prefers the path which is having shortest AS Path. ( If you want to skip this step, then you can give bgp bestpath as-path ignore)
--> Prefer the path with the lowest origin type
--> Prefer the path with the lowest multi-exit discriminator (MED).
--->Prefer eBGP over iBGP paths.
--> Prefer the path with the lowest IGP metric to the BGP next hop.
-->When both paths are external, prefer the path that was received first When both paths are external, prefer the path that was received first
-->Prefer the route that comes from the BGP router with the lowest router ID.
--> If the originator or router ID is the same for multiple paths, prefer the path with the minimum cluster list length.
-->Prefer the path that comes from the lowest neighbor address
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